An action of a typical grand piano is described (see, Non-Patent Document 1). In the following description, the front side seen from the piano player is referred to as “front”, the far side is referred to as “back”, the left side is referred to as “left”, and the right side is referred to as “right”. In addition, the expression “key is in its rest position” means that the front of a key is located at the highest point of its travel while the tail of the key is located at the lowest point of its travel.
A piano player depresses a key that is in its rest position. The tail of the key pushes up a wippen. A repetition lever and a jack raise a hammer roller, and a hammer pivots towards a string located above. Almost at the same time, a damper head rises and is released from its contact with the string.
The piano player further depresses the key. Immediately before the hammer reaches the string, a jack tail comes into contact with a regulating button. The jack pivots and a protruding end of the jack slips out from under the hammer roller.
Then, the hammer hits the string. It vibrates and produces a note. After hitting the string, the hammer rebounds and falls. At this point, the protruding end of the jack is no longer under the hammer roller. The hammer roller pushes down the repetition lever. The hammer falls back while receiving a force applied by a repetition spring. A back check catches the hammer.
Next, the piano player releases the key. The wippen falls and the hammer escapes from the back check. The repetition spring pushes up on the repetition lever and raises the hammer roller. As the wippen is at its lower position, the hammer rises slightly. Thus, the jack pivots by the force received from the jack spring. The protruding end of the jack moves back under the hammer roller. Accordingly, the piano player can depress the same key again and make the string vibrate to produce a note. The repetition lever comes into contact with a drop screw and stops the upward motion of the hammer. Subsequently, the hammer falls along with the wippen.
Because of the construction of grand pianos, the front of the key rises by approximately one third of the key dip distance from the lowest point of its travel to its rest position when the protruding end of the jack moves back under the hammer roller. In a grand piano, when the key rises by approximately one third of the key dip distance from the lowest point of its travel to its rest position, the piano player can depress the same key again and make the string vibrate to produce a note. According to a certain experiment that the present inventor knows, the piano player can play 14 repeated notes per second on the same key within a given period of time.
The unique key touch of the grand piano is provided with the following first to third forces. The first force is a force that is transmitted from a repetition spring to the key. The second force is a force that is transmitted to the key when the protruding end of the jack moves back under the hammer roller. The third force is a force that is transmitted to the key when the repetition lever comes into contact with the drop screw.
An action of a typical upright piano is described (see, Non-Patent Document 1).
A piano player depresses a key that is in its rest position. The tail of the key pushes up a wippen, and the wippen rotates. A protruding end of a pushing-up portion of a jack pushes up a pushed-up portion of a hammer butt. The hammer butt and a hammer pivot towards a string on a hammer butt flange. As the wippen rotates, a damper head is released from its contact with the string.
The piano player further depresses the key. The jack tail strikes a regulating button, and the jack pivots. Then, the protruding end of the pushing-up portion of the jack slips out from under the pushed-up portion of the hammer butt. The hammer is disengaged from the motion of the key. This disengagement is so-called “let-off”.
The hammer continues to move towards the string on its own inertia and hits the string, allowing it to vibrate. After hitting the string, the hammer rebounds from the string. A back check catches a catcher, which stops the motion of the hammer.
Next, the piano player releases the key. The wippen falls and the catcher escapes from the back check. In addition, the jack tail escapes from the regulating button. When the wippen completely falls, a gap is formed under the pushed-up portion of the hammer butt into which the protruding end of the pushing-up portion of the jack can be inserted. Then, the jack pivots by the force received from the jack spring. The protruding end of the pushing-up portion of the jack slips under the pushed-up portion of the hammer butt and they engage with each other.
Next, the gap required to engage the jack and the hammer butt in the upright piano is described.
The piano player depresses the key to the lowest point of its travel. Because of the construction of actions of the upright piano, the front of the key falls by approximately 10 mm, the tail of the key pushes up the heel of the wippen by approximately 5 mm, and the jack flange rises by approximately 5 mm. When compared with the key in its rest position, the protruding end of the pushing-up portion of the jack rises by approximately 5 mm after escaping from under the hammer butt. On the other hand, the hammer butt is pushed up by the jack and pivots on the hammer butt flange. The distance between the hammer butt flange and the pushed-up portion of the hammer butt is short. Thus, as the back check catches the catcher, the pushed-up portion of the hammer butt is raised only by approximately 1 mm from its rest position. The values given herein are merely examples. In the upright piano, the amount that the protruding end of the pushing-up portion of the jack is raised is significantly larger than the amount that the pushed-up portion of the hammer butt is raised. As a result, when the wippen falls completely and the key returns to its rest position, a gap is formed under the pushed-up portion of the hammer butt into which the protruding end of the pushing-up portion of the jack can be inserted. Until the key returns to its rest position, there is no such a gap under the pushed-up portion of the hammer butt.
If the protruding end of the pushing-up portion of the jack moves towards under the pushed-up portion of the hammer butt before the key returns to its rest position, the protruding end of the pushing-up portion of the jack hits a surface located in front of and above the pushed-up portion of the hammer butt. The protruding end of the pushing-up portion of the jack cannot be slipped under the pushed-up portion of the hammer butt. Thus, it is impossible to engage the jack and the hammer butt with each other.
When the jack and the hammer butt engage with each other, the piano player can depress the same key again and make the string vibrate to produce a note. According to the aforementioned experiment, the piano player can play 7 repeated notes per second on the same key within a given period of time. This means that the upright piano is inferior to the grand piano from the viewpoint to permit playing of repeated notes.
In addition, the action of the upright piano does not have the repetition lever, the repetition spring, the hammer roller and the drop screw. Thus, the touch of the keys of the upright piano is significantly different from the touch of the keys of the grand piano.
In upright pianos, improved actions have been suggested in order to permit more rapid playing of repeated notes on a single key.
One improvement of the action of the upright piano is, for example, as described below (see, Patent Document 1). This technique is referred to as a related art 1.
The action according to the related art 1 has a spring member provided on the pushing-up portion of the jack. When the pushing-up portion of the jack slips out under the pushed-up portion of the hammer butt, the spring member comes into contact with the regulating rail and forces the jack against the hammer butt.
When the piano player releases the key, the wippen and the jack move down. The jack pivots by the force received from the jack spring and the spring member. Then, the jack and the hammer butt engage with each other.
In addition, another improvement of the action of the upright piano is as described below (see, Patent Document 2). This technique is referred to as a related art 2.
In the action according to the related art 2, a compression coil is provided as a jack/repetition spring between the protruding end of the pushing-up portion of the jack and the catcher. When the pushing-up portion of the jack slips out under the pushed-up portion of the hammer butt, the jack/repetition spring forces the jack against the hammer butt. In addition, a hammer return spring is engaged with the hammer butt. The hammer return spring aids the motion of the hammer rebounding from the string after hitting it.
When the piano player releases the key, the wippen and the jack move down and the jack tail escapes from the regulating button. The jack pivots by the force received from the jack/repetition spring. Then, the jack and the hammer butt engage with each other.